1. Field of the Invention
The present invention relates to a lengthy volume hologram layer transfer foil formed length-wise to transfer a volume hologram layer continuously, to a method of producing a volume hologram laminate using the hologram layer transfer foil, and to a volume hologram laminate.
2. Disclosure of the Related Art
Holograms are those in which the wave front of an object light beam is recorded as interference fringes in a photosensitive material by the interference between two beams (object light beam and reference light beam) having the same wavelength, wherein, when a light beam having the same wavelength as a reference light beam used at the time of recording interference fringes is applied, causing a diffraction phenomenon by the interference fringes, whereby the same wave front as that of the original object light beam can be regenerated. The hologram has the advantages, such as in providing a beautiful appearance and in being difficult for reproduction and is therefore frequently used in security applications. Among these, in plastic cards typified by credit cards and cash cards, cards with hologram have come to be widely used from the viewpoint of, primarily, the prevention of reproduction and improvement in design.
Such a hologram can be divided into some types by the recording form of interference fringes. Typically, the hologram can be divided into a surface relief type hologram and a volume type hologram. Here, the surface relief type hologram is a type in which fine convexo-concave pattern is engraved on the surface of a hologram layer to record a hologram. The volume type hologram, on the other hand, is a type in which interference fringes produced by the interference of light are depicted three-dimensionally in the direction of the thickness as fringes differing in refractive index to record a hologram. Among these holograms, the volume type hologram has the advantage that reproduction is more difficult than in the case of the relief type hologram since the volume type hologram is a type in which a hologram image is recorded by a difference in the refractive index of materials, and therefore, the volume type hologram is expected to be used in applications for forgery preventive means used for securities, cards and the like.
Various methods are known corresponding to the subject provided with a hologram as a method of providing a hologram to, for example, securities and cards when a hologram is used for an improvement in design and forgery preventive means. As these methods, for example, a method in which slit-shaped holograms are knitted and a method in which holograms are embedded in a medium in such a manner that they are visible from the outside. However, a method in which holograms are applied to specified positions is generally used. Among these methods, a method in which holograms are transferred to an arbitrary substrate from a hologram layer transfer foil formed with holograms to thereby apply the holograms to specific positions have come to be widely used as a simpler method.
Here, plural materials differing in refractive index are generally used in the volume type hologram and a photopolymerizable material that can be polymerized by irradiating it with specified light is usually used. For this, it is known that the hologram layer in which volume type holograms are recorded tends to be increased in mechanical strength. The volume type hologram has such a nature that a hologram image is recorded by arranging differences in refractive index three-dimensionally and therefore, the thickness of the layer on which the hologram is formed tends to be larger than the relief type hologram. It is pointed out that the volume type hologram is poor in foil cuttability and it is difficult to use a method of transferring a volume type hologram by using the hologram layer transfer foil mentioned above.
In view of this situation, Patent Documents 1 and 2 disclose examples enabling the use of the transfer method using the above-mentioned hologram layer transfer foil even regarding the volume type hologram, by adjusting the breaking strain and breaking strength of the hologram layer in which the volume type hologram is recorded, to each specified value.    [Patent Document 1] Japanese Patent Application Laid-Open No. 3-46687    [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-070064